1. Field Of The Invention
The present invention relates to a sheet break detector apparatus. More specifically, the present invention relates to a sheet break detector apparatus for detecting a sheet break in a transfer of a paper machine dryer section.
2. Information Disclosure Statement
In the operation of a typical papermaking machine dryer section, the web or sheet of paper extending therethrough may break eight or more times a day.
When a web breaks, it is essential that such breakage be detected as soon as possible so that the web can be rethreaded.
Typically, when a break occurs in a dryer section, the loss of production amounts to around $40,000 per hour.
Furthermore, if a web breakage is not readily detected, there exists the problem of two dryer felts rubbing against each other, particularly in the case of a web transfer section in a Bel-Champ.TM. dryer section in which the web may be transferred without open draw between respective dryer sections. A Bel-Champ.TM. dryer section is taught in U.S. Pat. No. 4,934,067 assigned to Beloit Corporation.
Such scuffing between adjacent felts may result in burning one or the other of the felts.
Felts typically cost in the region of $40,000 each, and the downtime required to replace a felt may be several hours.
Accordingly, the present invention provides a simple means for quickly detecting a web breakage.
In the prior art, optical detecting systems have been employed, which include a photoelectric sensor. However, such photoelectric sensors require the provision of a felt having a color difference relative to the sheet or web in order for such photoelectric sensors to work efficiently.
Also, sensors have been provided which sense the vacuum level existing within a vacuum roll disposed upstream or downstream relative to the double felted web transfer section.
Such vacuum sensors do not work effectively if only a low vacuum exists within the vacuum transfer roll.
Also, such vacuum sensors would not operate if a grooved roll was substituted for the typical vacuum transfer roll.
Applicant has discovered that a beam of infrared light will freely pass through at least two dryer felts, but that such infrared beam will be blocked when a sheet or web of paper is interposed between the respective dryer felts.
Therefore, the present invention provides a sheet break detector apparatus which overcomes the aforementioned disadvantages of the aforementioned prior art arrangements and provides a detector apparatus which makes a considerable contribution to the art of drying a web in a paper machine dryer section.
A primary objective of the present invention is the provision of a sheet break detector apparatus which works efficiently regardless of the color of the dryer felt.
Another object of the present invention is the provision of a sheet break detector apparatus which operates independently of the existence of a vacuum applied to a vacuum transfer roll.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter, taken in conjunction with the annexed drawings.